The present invention relates to a pneumatic booster mounted on a brake apparatus for a vehicle, such as an automobile.
Generally, in a brake apparatus for an automobile, a pneumatic booster is provided to enable a large braking force to be generated. In the booster, a suction pressure of an engine is utilized as a negative pressure by being introduced into a constant-pressure chamber (a negative-pressure chamber) of the booster; and a thrust force is generated in a power piston due to a difference between the negative pressure in the negative-pressure chamber and an atmospheric pressure, thus enhancing a brake operating force.
Further, there is known a technique of using an ejector to supply a high degree of vacuum to a pneumatic booster. The ejector comprises a nozzle, a diffuser disposed downstream of the nozzle and a suction port (a vacuum pick-up port) provided between the nozzle and the diffuser. By flowing a gas through the nozzle towards the diffuser, a high-speed jet flow is generated, to thereby create a high degree of vacuum at the suction port.
Use of an ejector is especially advantageous where a supercharger, such as a turbocharger, is utilized as it enables a high power to be obtained from a small engine. When a supercharger is used, suction air is pressurized by the supercharger, which results in a lowering of the degree of a vacuum in a suction pipe of the engine. In such a case, an ejector is an effective means for increasing the degree of vacuum to be introduced to a pneumatic booster.
In conventional techniques, for example, as is indicated in Examined Japanese Patent Application Publication No. S63-39469, an ejector is provided as a separate body between a suction pipe of an engine and a pneumatic booster. Alternatively, as is indicated in Japanese Patent Application Public Disclosure No. 2002-211385, an ejector may be attached to the exterior of a pneumatic booster.